Extending Postharvest Vase Life of Dahlia: the Struggle Continues

Holly Scoggins, Leslie Peck, Margaret Aiken Department of Horticulture, Virginia Tech, Blacksburg

Benzyladenine and vase life ex- tension The inspiration for this research reallyWe grew two dahlia cultivars, ‘Park came when my graduate student, Les- Princess’ and ‘Karma Yin Yang’ (it is . Previous research has shown lie Peck, attended the ASCFG Grower fun to say “yin yang” in a scien- that cytokinins such as benzyladenine Intensive at Greenstone Fields in tific presentation) in drip-irrigated, (BA) can be an option for delaying September of 2015. The workshop mulched rows at our Urban Horticul- senescence of several species of cut included tours to Don’s Dahlias and ture Center (Blacksburg, Virginia, USDA flowers. One mechanism proposed is Wollam Gardens, where Leslie learned Hardiness Zone 6B, elevation 2,100 ft). the regulation of ethylene biosynthesis much about dahlia production, includ- Stems were harvested beginning 13 by BA, but other factors may be at work. ing their notoriously short vase life. She weeks from planting. For all studies, Researchers found applications of BA workcame onback Delphinium inspired to lookHelianthus at several vase life was defined as number of days (dip or spray) significantly extended postharvest aspects, in addition to her until at least 50% of the flower petals the vase life of dahlia ‘Kokucho.’ Our and . had wilted. work was done on the two dahlia cul- tivars mentioned above. After harvest, stems of each cultivar received one of three treatments: 5-second dip-1 of flower heads into BA at 300-1 mg·L , a water dip (BA at 0 mg·L ), or no dip treatment (dry). Vase life was not significantly impacted for either ‘Park Princess’ (ranged from 7 to 9 days) or ‘Karma Yin Yang’ (7 days) as measured amongEthylene these .treatments. So scratch that, at least for these cultivars. Dahlia is not usually included on lists of ethylene-sensitive flowers, but some research and anec- dotal evidence exists to the contrary. The cultivar ‘Kokucho’ was found to be sensitive to ethylene, the same researchers found application (dip or spray) of the endogenous plant hor- mone benzyladine (BA) significantly extended vase life. However, Dr. John Dole and crew had worked on extend- Ethylene treatment chamber. ing the postharvest life of dahlia ‘Karma Thalia’ and found that particular culti- The Cut Flower Quarterly 20 Volume 30, Number 3 μ ˡ - var to NOT be sensitive to ethyleneμ at 1.0ˡ L·L . The active Vase life of ‘Karma Yin Yang’ was not altered by flower threshold level for ethylene to have physiological- impactsμ stage. Waiting to harvest ‘Karma Yin Yang’ until flowers have on plantsμ is generally cited as 0.1 L·L . -1 fully opened will ensure flowers are open for the consumer To administer-1 the ethylene treatments (0.9 L·L but is not detrimental to postharvest longevity. Things got or 0 L·L for 18 hours), we built an airtight Plexiglas a bit more complicated with ‘Park Princess’: flowers har- chamber. Seam integrity was tested with a disco fog ma- vested when half open or earlier had significantly longer chine (science!). Air samples were taken at termination vase life than flowers harvested fully open. However, these of treatment to verify concentration via gas chromatogra- flowers failed to open completely in the vase. At five days af- Extending Postharvest Vase Life of Dahlia: the Struggle Continues phy. Vase life for both cultivars was similar to that in the BA ter harvest, flowers harvested at budbreak were significantly experiment, and not impacted by ethylene exposure. These less opened than flowers harvested when open, but flowers studies together suggest the effectiveness of BA in extend- harvested when open or half open were not significantly ing vase life of dahlia is tied to ethylene sensitivity and is different. For ‘Park Princess’, it may be preferable to harvest cultivar-dependent. flowers when they are half open due to improvements in What about ethylene sensitivity in other cultivars? We vase life with minimal impact on postharvest flower opening. Dr. Holly L. Scoggins is worked with a local grower to obtain stems of dahlia ‘Amber an Associate Professor, Dept. of Horticulture, Virginia Tech. Queen,’ ‘Bodacious,’ ‘Bride to Be,’ ‘Cherish,’ ‘Ginger Willow,’ μ Leslie Peck graduated ‘Lollipop,’ ‘Park Princess,’ and ‘White-1 Fawn.’ All were exposed from Virginia Tech with an M.S. in Horticulture and is now to ethylene levels of 0.8-0.9 L·L for 18 hours each. Ethyl- μ an Extension agent in Forsyth County, North Carolina. ene exposure did not alter vase life in any-1 of the cultivars Margaret Aiken studied when compared to control (0 L·L ). Vase life was, was our Research Technician extraordinaire. however, Water widely/wildly temperature variable. among cultivars, ranging from 3.8 days for ‘Amber Queen’ to 9.5 days for ‘Bodacious.’ Many thanks to the fabulous ASCFG Research Foundation Some sources suggest that plac- for fiscal support of our research, and Brent and Becky’s ing freshly cut dahlias into hot water will encourage water Bulbs for the dahlia tubers. uptake and extend vase life. In a replicated experiment, flowers were harvested when 50% to 75% of the petals had expanded. Stems were rapidly recut and placed immediately into water that was either ambient temperature (20 to 23°C) Grants Available for Cut Flower Research or heated to 36-43°C. The hot water treatment significantly increase water uptake for both cultivars and increased vase life for ‘Park Princess’ from 4.0 to 6.0 days, though the dif- The ASCFG Research Foundation is pleased to ference between temperature treatments was not significant announce the continuation of its Competitive for ‘Karma Yin Yang’ (5.5 to 6.3 days). When the experiment Research Grant program. This year, the fund will was repeated the following week, water temperature had provide one or more grants totaling $8000. no impact on either water uptake OR vase life, for either cultivar! We did note the weather during the second harvest The competition is open to academic and was cooler and drier with lower relative humidity. Alas, frost governmental researchers. Horticulture and came before we could run a third “tiebreaker” experiment. floriculture extension agents are encouraged to Our results were inconclusive: the hot water treatment is apply, and to consider conducting research on F probablyHarvest not stageworth. the trouble, though growers might want cooperating cut flower farms. to give it a try for some cultivars with very short vase life. ind details under the “Research” tab at ascfg.org Dahlia for local markets are cut mostly to fully open. But some can be cut quite early; performance seems to be cultivar-dependent. For this study, our field- grown dahlia ‘Park Princess’ and ‘Karma Yin Yang’ were harvested at the following stages: —Budbreak: flower head showing color with at least one petal lifted from the bud but less than 5% of flower petals expanded. —Half open: intermediate stage of opening. —Open: flower head almost completely open. 80% to 95% of petals expanded.

The Cut Flower Quarterly 21 Volume 30, Number 3